Fiberoptic data transmission systems, such as for voice and data communications, typically employ receivers having some type of optical-to-electrical converter to receive optical pulses from the fiberoptic. An example of such an optical-to-electrical converter is an avalanche photo diode or APD. Typical receivers employing such a photo diode often have a bias control circuit for the photo diode that includes one or more potentiometers in order for the APD bias voltage to be set at a suitable level. As explained more fully herein, APDs typically have gain and noise characteristics that vary depending upon the particular photo diode and the particular bias voltage applied to the APD. Moreover, the characteristics of the APD tend to vary as a function of temperature and with the age of the APD. Still another problem relates to APD and overall receiver performance as a function of power supply variations.
Designers have attempted to address such problems with various bias control and other circuits, typically employing potentiometers or other manual adjustment techniques. The manufacturing and calibration of such receivers, however, tends to be laborious, time consuming and error prone. Additionally, many such receivers tend to operate reliably only in limited temperature ranges, with the result being that undesirable temperature conditions may lead to undesirable error levels or the necessity for expensive temperature control measures or periodic maintenance.
In general, conventional fiberoptic receivers have tended to operate reliably over limited temperature and voltage ranges, while providing limited manual adjustments such as by way of potentiometers and the like. Additionally, such conventional receivers tend to have limited overcurrent protection, and in general do not provide user programmability, except by tedious adjustment of potentiometers and the like.